Cushman, et al. in U.S. Pat. No. 4,052,511 discloses angiotensin converting enzyme inhibitors of the formula ##STR4## wherein R.sub.1 and R.sub.4 each is hydrogen, lower alkyl or phenyl lower alkyl;
R.sub.2 is hydroxy, amino, hydroxyamino or lower alkoxy; PA0 and n is 0 to 2. PA0 Ondetti, et al. in U.S. Pat. No. 4,105,776 disclose angiotensin converting enzyme inhibitors of the formula ##STR7## wherein R.sub.1 is hydrogen or lower alkyl; PA0 R.sub.2 is hydrogen, R.sub.5 -CO--, R.sub.6 -S-- or R.sub.7 ; PA0 R.sub.5 is lower alkyl; PA0 R.sub.6 is lower alkyl PA0 n is 0, 1 or 2; PA0 and R.sub.7 is ##STR8## PA0 R.sub.2 is hydrogen, lower alkyl, phenyl lower alkyl or halo substituted lower alkyl; PA0 n is 0, 1 or 2; PA0 X is --(CH.sub.2).sub.m Z--; PA0 Z is oxygen, sulfur or imino; PA0 m is 0 or 1; PA0 Y is --S--R or ##STR10## R is hydrogen, lower alkyl, ##STR11## R.sub.3 is lower alkyl, phenyl or phenyl lower alkyl; and R.sub.4 is hydroxy, amino, hydroxyamino or lower alkoxy. PA0 Y is S--R; PA0 R is ##STR33## R.sub.3 is lower alkyl; R.sub.2 is phenyl lower alkyl or hydrogen; PA0 R.sub.1 is lower alkyl; PA0 n is 1; PA0 R is hydrogen; PA0 R.sub.2 is phenyl lower alkyl or hydrogen; PA0 R.sub.1 is lower alkyl; PA0 n is 1; m is 0; and Z is oxygen. PA0 R is hydrogen; PA0 R.sub.2 is phenyl lower alkyl or hydrogen; PA0 R.sub.1 is lower alkyl; PA0 n is 0; PA0 m is 0; PA0 and Z is oxygen. PA0 R.sub.1 is lower alkyl; PA0 n is 1; PA0 m is 0; PA0 and Z is oxygen. PA0 R.sub.1 is lower alkyl; PA0 n is 0; PA0 m is 0; PA0 and Z is oxygen. ##STR36## R.sub.4 is lower alkoxy; R.sub.2 is phenyl lower alkyl or hydrogen; PA0 R.sub.1 is lower alkyl; PA0 n is 0; PA0 m is 0; PA0 and Z is oxygen. PA0 n is zero and R.sub.2 is hydrogen, PA0 and wherein R.sub.1 is methyl, PA0 n is one and R.sub.2 is hydrogen.
Ondetti, et al. in U.S. Pat. No. 4,154,935 discloses hyportensive agents of the formula ##STR5## wherein R is hydrogen, lower alkanoyl or ##STR6## R.sub.3 and R.sub.4 is each hydrogen, lower alkyl or trifluoromethyl; and n is 0 or 1.